Current-voltage relation for superconducting d-wave junctions

We calculate the current-voltage (I-V) relation for planar superconducting d-wave junctions for both arbitrary transmission of the junction and arbitrary orientation of the d-wave superconductors. The midgap states (MGS) present at interfaces/surfaces of a d-wave superconductor influence the I-V relation. In some arrangements we find considerable negative differential conductance and lower threshold voltage for non-zero current due to resonant conduction through MGS.